BST capacitors have essentially been developed for radio applications, in particular for mobile telephony. Having a capacitor with an analog-adjustable capacitance significantly improves performance, since it enables to adapt the device comprising such a capacitor to the outer environment.
A BST capacitor conventionally appears in the form of an integrated circuit comprising at least three terminals, two terminals corresponding to the capacitor electrodes, intended to be connected to the radio frequency application, and one terminal of application of a DC bias potential. The capacitance of a capacitor is set by the value of the DC bias potential which is applied thereto, generally in a range from a few volts to a few tens of volts, typically between 2 and 20 volts.
The bias voltage of a BST capacitor is generally provided by a dedicated control circuit, performing a high-voltage digital-to-analog conversion, that is, converting a digital configuration word (generally, a byte) into a DC analog voltage to be applied to the capacitor to set the capacitance thereof.
The control or configuration of a BST capacitor now suffers from inaccuracies due, among others, to manufacturing tolerances and temperature-related variations and variations related to the capacitor hysteresis.